1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to an air cooled turbine airfoil with relatively low cooling flow volume.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
In a gas turbine engine, airfoils such as stator vanes (sometimes referred to as guide nozzles) and rotor blades are exposed to extremely high temperature gas flows in order to produce a high efficient conversion of the combustion gas. In order to allow for higher temperature, the airfoils exposed to the higher temperatures require internal and external cooling. Elaborate internal cooling circuits have been designed to produce convection cooling for the airfoils, and film cooling holes are used to provide a layer of film cooling air over certain external surfaces of the airfoil to limit exposure to the hot gas flow. An airfoil with many film cooling holes requires a larger volume of cooling air flow because much of the cooling air is discharged out from the airfoil before passing through much of the airfoil internal cooling circuit.
In future industrial gas turbine engines, large airfoils are proposed in which the latter stages will also require some sort of internal cooling in order to increase the useful life of the airfoils. In recent engines, typically only the first and second stages of the turbine require internal cooling while the last two stages (third and fourth) are not cooled at all.